A refrigeration system having a compressor which compresses a refrigerant and an expander which expands the refrigerant as separate components is disclosed, for example, in Patent Document 1. This refrigeration system includes a refrigerant circuit in which the compressor and the expander are connected to each other to circulate the refrigerant and run a refrigeration cycle. The compressor includes a compression mechanism, and an electric motor for driving the compression mechanism. The expander includes an expansion mechanism which generates rotational power as the refrigerant expands, and an electric generator connected to the expansion mechanism via an output shaft. The electric generator is driven by the rotational power from the expansion mechanism, and generates electricity. The generated electric power is supplied to the electric motor of the compressor and is used to drive the compression mechanism.